1. Field of Invention
The present invention relates to improvements in multiple layer steel (MLS) cylinder head gaskets for automotive internal combustion engines, including gaskets having stopper layers situated closely adjacent combustion cylinder bore edges, and particularly for providing enhanced sealing between cylinder bores.
2. Description of the Prior Art
Those skilled in the art will appreciate the issues involved in maintaining a high quality seal between cylinder apertures of a cylinder block in an internal combustion engine and a cylinder head fastened to the block. In recent years, MLS cylinder head gaskets have become a preferred design choice, wherein all (typically at least three) gasket layers have been formed of steel. Beaded exterior layers have generally been fabricated of 301 stainless steel, a relatively robust metal with a high spring rate for meeting requisite performance requirements over useful gasket life. The center layer, also called a “spacer” layer, has generally been formed of less robust metals, such as 409 stainless steel, or in some cases even zinc-plated or plain low carbon steels, for meeting less rigorous operating requirements.
It is desirable that areas immediately adjacent circumferential edges of engine cylinder bores be subject to considerably greater stresses for assuring proper sealing than areas of the gasket radially remote from the apertures. To meet the greater stress requirements at the bore edge areas, so-called stopper layers have been employed in areas that circumferentially surround each cylinder bore. The stopper layers are purposefully designed to provide increased sealing pressures around the noted areas surrounding the combustion apertures. In some cases the stoppers have been formed of extra layers of metal, consisting either of layers folded over or under primary sealing layers. In other cases, the stoppers have been formed as layers separately provided, e.g., discrete annular rings positioned about the aperture boundaries.
Still in other cases, embossed resilient sealing beads are employed in duplicate mirror image exterior sealing layers. In some instances, beaded exterior sealing layers have been prone to cracking at the boundaries of the beads, particularly in narrow web regions between cylinder bores. In small area regions, high stress dynamics can create stresses on the beads that can exceed bead deflection stress capabilities. Resultant cold working and associated bead cracking are issues seriously detrimental to both the performance and longevity of gaskets that otherwise provide reliable combustion sealing media. An improved resilient sealing bead structure would be welcomed by the industry; particularly, one having a web area stopper structure designed to maintain adequate pre-stresses within the bolted joint during useful life of the gasket with lower risks of bead cracking.